Method of producing multi-wavelength semiconductor laser device

Abstract

A method for producing a multi-wavelength semiconductor laser device includes the steps of: forming a nitride epitaxial layer on a substrate for growth of a nitride single crystal; separating the nitride epitaxial layer from the substrate; attaching the separated nitride epitaxial layer to a first conductivity-type substrate; selectively removing the nitride semiconductor epitaxial layer to expose a portion of the first conductivity-type substrate and to form a first semiconductor laser structure; and sequentially forming second and third semiconductor laser structures on the exposed portion of the first conductivity-type substrate.

1. A method for producing a multi-wavelength semiconductor laser device, comprising the steps of:
 preparing a substrate for growth of a nitride single crystal thereon; 
 sequentially growing a first conductivity-type first clad layer, a first active layer and a second conductivity-type first clad layer on the substrate, to form a nitride epitaxial layer; 
 separating the nitride epitaxial layer from the substrate; 
 attaching the separated nitride epitaxial layer to a first conductivity-type substrate; 
 selectively removing the nitride epitaxial layer such that a portion of the substrate is exposed, to form a first semiconductor laser structure; 
 sequentially growing a first conductivity-type second clad layer, a second active layer and a second conductivity-type second clad layer on the exposed portion of the first conductivity-type substrate, to form a second semiconductor laser structure separated from the first semiconductor laser structure; 
 sequentially growing a first conductivity-type third clad layer, a third active layer and a second conductivity-type third clad layer on the remaining portion of the first conductivity-type substrate, to form a third semiconductor laser structure separated from the first and second semiconductor laser structures; and 
 forming a first electrode connected to a bottom surface of the first conductivity-type substrate and forming second electrodes connected to the respective second conductivity-type clad layers of the first, second and third semiconductor laser structures. 
 
     
     
       2. The method according to  claim 1 , further comprising the steps of: selectively etching the respective second conductivity-type clad layers of the first, second and third semiconductor laser structures, after the formation of the third semiconductor laser structure and before the formation of the first electrode and the second electrodes, to form ridge-shaped layers, and forming an insulating layer on top surfaces of the second conductivity-type clad layers except for top ends of the ridge-shaped layers wherein the second electrodes are connected to the respective second conductivity-type clad layers through the top ends of the ridge-shaped layers. 
     
     
       3. The method according to  claim 2 , wherein the insulating layer is formed in such a manner that it is extended to side faces of the first, second and third semiconductor laser structures. 
     
     
       4. The method according to  claim 2 , wherein the insulating layer is formed of SiO 2  or Si 3 N 4 . 
     
     
       5. The method according to  claim 1 , wherein the separation of the nitride epitaxial layer from the substrate is performed by irradiating the bottom surface of the substrate with laser light to lift-off the nitride epitaxial layer. 
     
     
       6. The method according to  claim 5 , wherein the step of separating the nitride epitaxial layer comprises the sub-step of lapping the bottom surface of the substrate for growth of a nitride single crystal, before the laser irradiation, to decrease the thickness of the substrate. 
     
     
       7. The method according to  claim 1 , wherein the attachment of the nitride epitaxial layer to the first conductivity-type substrate is performed by pressuring the nitride epitaxial layer on a top surface of the first conductivity-type substrate at high temperature. 
     
     
       8. The method according to  claim 1 , wherein the step of forming the second semiconductor laser structure comprises the sub-steps of:
 sequentially growing the first conductivity-type second clad layer, the second active layer and the second conductivity-type second clad layer on the top surface of the first conductivity-type substrate on which the first semiconductor laser structure is formed, to form an epitaxial layer for the second semiconductor laser structure; and 
 selectively removing the epitaxial layer for the second semiconductor laser structure, to form the second semiconductor laser structure separated from the first semiconductor laser structure on a portion of the first conductivity-type substrate. 
 
     
     
       9. The method according to  claim 1 , wherein the step of forming the third semiconductor laser structure comprises the sub-steps of:
 sequentially growing the first conductivity-type third clad layer, the third active layer and the second conductivity-type third clad layer on the top surface of the first conductivity-type substrate on which the first and second semiconductor laser structures are formed, to form an epitaxial layer for the third semiconductor laser structure; and 
 selectively removing the epitaxial layer for the third semiconductor laser structure, to form the third semiconductor laser structure separated from the first and second semiconductor laser structures on a portion of the top surface of the first conductivity-type substrate. 
 
     
     
       10. The method according to  claim 1 , wherein the first, second and third semiconductor laser structures are formed in this order from one side of the first conductivity-type substrate. 
     
     
       11. The method according to  claim 1 , wherein the substrate for growth of a nitride single crystal is a sapphire, SiC, or GaN substrate, and the nitride epitaxial layer is formed of a GaN-based semiconductor material. 
     
     
       12. The method according to  claim 1 , wherein the first conductivity-type substrate is a first conductivity-type GaAs substrate, the epitaxial layer for the second semiconductor laser structure is formed of an AlGaAs-based semiconductor material, and the epitaxial layer for the third semiconductor laser structure is formed of an AlGaInP-based semiconductor material.